Created attachment 143026 [details]
the dmesg got after issue happened.
VGA of Host Machine:
00:02.0 VGA compatible controller : Intel Corporation Device [8086:3e9b] (prog-if 00 [VGA controller])
Monitor: Dell P2317H (can also reproduce it on other monitor)
steps to reproduce:
1. connect external monitor
2. see screen on external monitor
3. get flicker on external monitor
4. switch display mode by "windows+p" still get flicker or even dark screen.
5. see error message on dmesg
[drm:intel_dp_get_link_train_fallback_values [i915]] *ERROR* Link Training Unsuccessful
this issue could be also reproduced by main line kernel 5.0.0-rc1
Please try to reproduce the error using drm-tip (https://cgit.freedesktop.org/drm-tip) and kernel parameters drm.debug=0x1e log_buf_len=4M, and if the problem persists attach the full dmesg from boot.
Created attachment 143148 [details]
dmesg from drm-tip 2019-01-18
No more "[drm:intel_dp_get_link_train_fallback_values [i915]] *ERROR* Link Training Unsuccessful" but I still observe the issue.